1. Field of the Invention
This invention relates to semiconductor devices and in particular to a process for bonding a semiconductor device directly to the leads from the package containing the device without the use of lead wires, and to the resulting structure.
2. Description of the Prior Art
One of the most expensive steps in the production of a semiconductor device, and in particular in the production of an integrated circuit, is electrically connecting the semiconductor chip to the leads from its package. Typically this is done by bonding the semiconductor chip to the bottom part of the package and then bonding lead wires from bonding pads (sometimes called contact pads) on the chip to the corresponding leads from the package. To form each connection between a bonding pad and the corresponding lead, a person must first direct a bonding tool to the pad and form a bond between the lead wire and the pad, and then direct the bonding tool to the package lead and bond the other end of the lead wire to this package lead. The formation of such electrical connections between the chip and the package leads is an expensive, time-consuming operation. After these bonding operations are completed, the top is placed on the package.
Automatic techniques to carry out this bonding have been proposed. One such technique places the semiconductor chip face down on the surface of a substrate having electrically-conductive package leads placed thereon. Bonding pads on the chip, which typically support solder bumps, are located above the ends of the package leads. Unfortunately, the fact that the solder bumps are face down and thus not visible makes it expensive to accurately align the bumps with the underlying leads and impossible to inspect visually the resulting bonds. Moreover, the thermal contractions of the package leads after the bumps have been melted and soldered to the package leads can induce thermal stresses in the device which reduce its reliability.
Another proposed technique places the semiconductor die onto package leads contained in a lead frame. An operator, using a split microscope showing both the bottom and top of the die, visually aligns the bumps on each die with the corresponding leads. The die and leads together are then heated to solder the die to the leads. Again, however, the leads are such that stresses are often induced in the bumps, leads or die after the leads have been soldered to the bumps. In addition, the operator must place each die onto its corresponding set of leads and then heat the die separately to form the bonds. Although not as time-consuming as having the operator form lead-wire connections between each die and its package leads, this is still an expensive and time-consuming operation.